fix(i18n): Use ellipsis instead of triple dots on UserMigration messages

[DerDreschner]

I previously introduced triple dots in my user migration services. This breaks the translations pipeline via Transifex. Instead, I now use the ellipsis character as requested.

Fixes #13819

🤖 AI (if applicable)

• The content of this PR was partly or fully generated using AI (N/A)

[DerDreschner]

/backport to stable5.13

[rakekniven]

@DerDreschner According to our guidelines there should be a nbsp before the ellipsis. See https://docs.nextcloud.com/server/latest/developer_manual/basics/translations.html#dos-and-don-ts

[backportbot]

The backport to stable5.13 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable5.13
git pull origin stable5.13

# Create the new backport branch
git checkout -b backport/13820/stable5.13

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick af1371a3

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/13820/stable5.13

Error: Failed to check for changes with origin/stable5.13: No changes found in backport branch

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Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.